1. Field of the Invention
The present invention relates to a carbon nanotube field emitter electrode. More particularly, the present invention relates to a field emitter electrode having a novel structure which not only improves the adhesive strength of carbon nanotubes but also exhibits improved contact resistance, and a method for fabricating the field emitter electrode.
2. Description of the Related Art
Generally, field emission devices are light sources for emitting electrons in a vacuum environment, and use the principle that electrons emitted from fine particles are accelerated by a strong electric field to collide with fluorescent substances, thus emitting light. Such field emission devices provide superior luminescence efficiency and are compact and lightweight, compared to light sources for general illuminators, such as incandescent lamps. In addition, since field emission devices do not use heavy metals, unlike fluorescent lamps, they have the advantage of being environmentally friendly. For these reasons, field emission devices have drawn attention as next-generation light sources for various illuminators and display devices.
The performance of field emission devices is mainly determined by emitter electrodes capable of emitting a field. In recent years, a carbon nanotube (CNT) has been widely used as an electron-emitting material for emitter electrodes having excellent electron emission properties.
However, carbon nanotubes have a problem in terms of non-uniform growth on a large-area substrate. In an attempt to solve this problem, carbon nanotubes grown by a separate process are purified before adhesion to the substrate. Representative methods for fabricating a carbon nanotube emitter electrode include common printing and electrophoresis.
The fabrication of a carbon nanotube emitter electrode by printing is carried out in accordance with the following procedure. First, an electrode material is coated on a smooth substrate to form an electrode layer. Then, a paste of carbon nanotubes and a silver powder is printed on the electrode layer. The resulting structure is subjected to an annealing process to remove the resin and the solvent present in the paste. The annealed structure is subjected to taping to partially expose the carbon nanotubes to the surface.
However, the conventional method has the problems that the procedure is complicated and uniform dispersion of the carbon nanotubes is difficult, thus deteriorating the characteristics of the final field emitter electrode. In addition, sufficient physical and mechanical adherence of the paste to the underlying electrode material cannot be achieved by known paste printing processes.
On the other hand, the fabrication of a carbon nanotube emitter electrode by electrophoresis is carried out by the following procedure. Referring to FIG. 1, first, previously purified carbon nanotubes and a dispersant (e.g., a cationic dispersant) are mixed in an electrolytic solution. Then, a predetermined voltage is applied to both electrodes immersed in the electrolytic solution to adhere the carbon nanotubes to a substrate formed on the cathode.
The use of electrophoresis enables the carbon nanotubes to be relatively uniformly dispersed in the electrolytic solution, and simplifies the overall procedure. However, the conventional method has the problem that the carbon nanotubes are susceptible to mechanical impact because of their poor adhesive strength to the substrate.
In addition, since a large quantity of organic components remain on the electrically conductive polymer constituting the emitter electrode, they are likely to be oxidized once the emitter electrode is operated, which largely deteriorates the field emission properties. In extreme cases, undesired gases may be generated in an electron emission space where a vacuum is required, seriously degrading the performance of the field emission device.